This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 12 |
| 4 | 82 |
| 5 | 454 |
| 6 | 2912 |
| 7 | 18652 |
| 8 | 124299 |
| 9 | 841400 |
| 10 | 5800725 |
| 11 | 40506816 |
| 12 | 286137616 |
| 13 | 2040430976 |
| 14 | 14670243774 |
| 15 | 106225269954 |
| 16 | 773958961125 |
| 17 | 5670067999156 |
| 18 | 41742291894425 |
| 19 | 308645064367896 |
| 20 | 2291123920091484 |
| 21 | 17067970534656790 |